In general, a light emitting device is a compound semiconductor having a characteristic of converting electrical energy into light energy. The light emitting device may include compound semiconductors belonging to group III and V on the periodic table. The light emitting device can represent various colors by adjusting the composition ratio of the compound semiconductors.
When forward voltage is applied to the light emitting device, electrons of an N layer are combined with holes of a P layer, so that energy corresponding to band gap energy between a conduction band and a valance band may be diverged. The energy is mainly emitted in the form of heat or light. In the case of the light emitting device, the energy is diverged in the form of light. For example, a nitride semiconductor represents high thermal stability and wide band gap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and ultraviolet (UV) light emitting devices employing the nitride semiconductor have already been commercialized and extensively used.
The conventional nitride semiconductor is formed by sequentially laminating a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer on a substrate formed of sapphire.
However, the defect due to the potential incurs because of the difference in lattice constant between the sapphire used as the substrate and gallium nitride (GaN), which causes a problem that electrical characteristics and optical characteristics of the light emitting device are deteriorated.